This application relates to refrigerant cycles wherein performance enhancement is achieved by the use of an additional heat exchanger, and a split in the refrigerant flow. The disclosed embodiments provide performance enhancement not unlike an economizer cycle, but without the requirement of modification of the compressor.
Refrigerant cycles are utilized to provide cooling or heating. In a conventional refrigerant cycle, a compressor compresses a refrigerant and delivers a compressed refrigerant to a downstream condenser. From the condenser, the refrigerant passes through an expansion device, and from the expansion device to an evaporator. The refrigerant from the evaporator is returned to the compressor. The condenser may also be known as an outdoor heat exchanger and the evaporator as an indoor heat exchanger, when the system operates in a cooling mode. In a heating mode, their functions are reversed.
A refrigerant cycle is able to provide a certain amount of cooling or heating, known as the capacity. One way to increase the capacity of a refrigerant cycle is the use of an economizer circuit. In an economizer circuit, flow downstream of the condenser is split into a main flow and a secondary flow. The secondary flow is passed through an expansion device, which lowers the temperature of the secondary flow. The secondary flow and the main flow are then both passed through an economizer heat exchanger. The main flow is thus cooled, and when it reaches the evaporator, it has an increased cooling capacity. The secondary flow is returned to an intermediate compression point in the compressor. The economizer circuit does provide performance enhancements, however, in some applications the economizer cycle has been seen as too expensive to implement. In particular, the use of the economizer cycle does require modifications to the compressor to receive the returned refrigerant at the intermediate compression point.
One other way to enhance capacity is the use of an auxiliary liquid line-t-suction line heat exchanger. In such a concept, refrigerant downstream of the condenser is passed through the auxiliary heat exchanger, and the refrigerant returning from the evaporator back to the compressor is also passed through this heat exchanger. The refrigerant returning from the evaporator to the compressor cools the refrigerant leaving the condenser, which increases system capacity. However, the amount of performance enhancement provided by such systems is not always as great as would be desirable, mainly due to an associated undesirable increase in refrigerant temperature as it enters the compressor suction port.
In disclosed embodiments of this invention, refrigerant downstream of a condenser is broken into two flow paths. The two flow paths provide a main flow and a secondary flow. An auxiliary heat exchanger is positioned downstream of the condenser. The invention includes two distinct ways of splitting and recombining the flow, as well as two distinct ways of passing refrigerant through the auxiliary heat exchanger. However, the two embodiments are common in that the combined refrigerant flow is all returned to the suction port of the compressor.
In a first embodiment, the refrigerant is split downstream of the auxiliary heat exchanger into main and secondary flow paths. The main flow passes through the expansion device and evaporator. Downstream of the evaporator, this main flow is combined with a secondary tapped flow. The secondary tapped flow passes through the auxiliary expansion device but not through the evaporator. This secondary flow is still in a two-phase state, and is predominantly a liquid. The recombined flow is then passed through the auxiliary heat exchanger. Some superheat reduction of the recombined flow as compared to the main flow occurs during this mixing. In this manner, when the combined flow passes back through the auxiliary heat exchanger, it is able to cool the refrigerant downstream of the condenser to a greater extent than the prior art. Additionally, re-routing a secondary flow around the evaporator may benefit system performance as refrigerant pressure drop in the evaporator is reduced.
In a second embodiment, the refrigerant is split downstream of the condenser but upstream of the auxiliary heat exchanger. The secondary flow is passed through an expansion device, and then passed through the auxiliary heat exchanger to cool the main flow. However, the refrigerant is returned to the main suction line leading to the compressor suction port. In this regard, it is not unlike a standard economizer circuit. This second embodiment provides similar benefits to the system performance as the first embodiment, as it also does not require modifications to the compressor.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.